1. Field of the Invention
This invention relates to a soft magnetic thin film used as, for example, a core material for a magnetic head. More particularly, it relates to a novel soft magnetic amorphous alloy thin film having a high magnetic flux density and a high electrical resistivity.
2. Related Art Statement
In a magnetic recording/reproducing apparatus, such as a video tape recorder (VTR), research towards raising the density or the frequency of the recording signals for improving the image quantity is progressing. In keeping pace therewith, research and development of a so-called metal tape in which powders of magnetic metals, such as Fe, Co or Ni, are used as magnetic powders, or a so-called evaporated tape, in which a magnetic metal material is directly deposited by, for example, vacuum evaporation, on the base film, is advancing briskly.
Meanwhile, it may be contemplated that, with the tendency towards a higher coercivity of the magnetic recording medium, a higher saturation magnetic flux density is required of the material for a magnetic head employed for recording and/or reproduction. The ferrite material, which is frequently employed as the magnetic head material, has only a low saturation magnetic flux density, such that it is difficult to produce a soft magnetic material having a saturation magnetic flux density exceeding 5000 Gauss, so that it is difficult to cope with the tendency towards a higher coercivity of the recording medium satisfactorily.
With this in view, there has also evolved a composite magnetic head in which a magnetic core of the magnetic head is of a composite structure of ferrite or ceramics, and in which soft magnetic thin films having a high saturation magnetic flux density abut on each other to form a magnetic gap, i.e. a thin film magnetic head, in which magnetic cores and coils are formed by a thin film technique and are sandwiched with insulating films in-between to form a multi-layered structure.
As the soft magnetic thin films, there are known an Fe-Al-Si alloy magnetic thin film (so-called Sendust thin film) having a high saturation magnetic flux density, or a permalloy thin film. However, these soft magnetic metallic thin films exhibit a low electrical resistivity of not higher than 100 microhm/cm, because they are of an alloy material, and are deteriorated in magnetic characteristics in the high frequency range, above all, in the frequency range of the order of megahertzes, on account of eddy current losses. Such a deterioration in magnetic characteristics in the high frequency range is extremely inconvenient in view of the required high density recording that is recording at shorter wavelengths.
There has also evolved metal-metalloid amorphous alloy magnetic thin films, such as Fe-B, Fe-Si-B or Fe-Co-Si-B thin films, which are produced by a liquid quenching method or a gas phase quenching method. These films are of a single-phase amorphous structure, which may be said to be a homogeneous structure. The electrical resistivity of these films, while being higher than that of the thin films of Sendust, which is a crystal soft magnetic material, is at most 150 microhms/cm or thereabouts, while their saturation magnetic flux density is 11000 Gauss or thereabouts.
In general, for raising the saturation magnetic flux density of the conventional soft magnetic thin films, it is necessary to increase the amount of magnetic metals, such as Fe or Co, as a result of which the electrical resistivity is lowered. This means that the saturation magnetic flux density and the electrical resistivity represent contradictory properties in the case of the soft magnetic thin films formed of a magnetic alloy material, such that it has been difficult to achieve a high saturation magnetic flux density and a high electrical resistivity simultaneously.
There is also proposed by the present Applicant a method of forming a magnetic film by mixing a magnetic metal material and an insulating material by sputtering, such as a FeCoBN film as described in U.S. Pat. No. 4,620,961 or an FeCoBC or FeCoB.sub.2 C.sub.3 film as described in U.S. Ser. No. 279,244 corresponding to GB 2198146A.
These soft magnetic thin films, while exhibiting properties superior to those of the aforementioned magnetic alloy thin films or the one-phase amorphous thin films, still leave much to be desired. For example, the FeCoBN and FeCoB.sub.2 C.sub.3 materials are not satisfactory in soft magnetic properties, whereas the FeCoBC materials are not satisfactory in electrical resistivity.